The earliest events following mucosal HIV-1 exposure represent a critical window of opportunity for vaccine-elicited immune responses to impact the acquisition and propagation of HIV-1 infection. However, very little is known about the biology of the eclipse phase of HIV-1 infection in humans, particularly the immunologic and virologic events that occur at the mucosal site of transmission. Given the difficulties in studying the earliest mucosal events of HIV-1 infection in humans, modeling these events in nonhuman primates is required. Such studies will provide insight into the early events of virus transmission and the capacity of immune responses to block or to attenuate these events. In this Project, we hypothesize that SIV-specific immune responses elicited by adenovirus and poxvirus vaccine vectors will substantially impact the early events following intravaginal (IVAG) SIV infection of rhesus monkeys. In particular, we hypothesize that vaccine-elicited mucosal immune responses at the site of inoculation will limit the initial local amplification of virus at the mucosal portal of entry during the eclipse phase of infection prior to systemic virus dissemination. The goal is to define precisely when and where innate and adaptive immune responses intercept the virus following IVAG SIV infection of both .naive and vaccinated animals. To evaluate these hypotheses, we propose the following Specific Aims: 1. To define the early virologic, immunologic, and pathologic events following IVAG SIV infection of naive, unvaccinated rhesus monkeys; 2. To evaluate the capacity of adenovirus vector-based vaccines to impact the early events following IVAG SIV infection of rhesus monkeys;and 3. To assess the capacity of poxvirus vector-based vaccines to impact the early events following IVAG SIV infection of rhesus monkeys.